//‘Reasonable person’ …. it’s conceivable that a BAME person could find a joke about it pretty offensive.//
A reasonable person, of whatever colour or creed, would laugh because the joke is actually on Del Boy and his ignorance. Similarly with Alf Garnet, Rigsby, etc, We laughed at THEM. A French lady of my axcquaintance used to get very upset by 'Allo 'Allo because such was her penchant for bristling huffily at any perceived insult, she failed to recognise that all nationalities involved were being ridiculed. In her head it was just the French - Rene & Co being lead characters - and French. The moral of this story, I suppose, is what's in your head isn’t necessarily what's happening.